Ambient light sensing has traditionally been used in industrial applications involving photometry, and over the years was incorporated in some consumer electronics appliances involving displays such as LCDs, FPDs, plasma displays, HDTVs, computer displays, camcorders etc., for brightness control. Lately, the concept has started to appear in handheld devices such as PDAs, MP3 players, PMP players and mobile phones. The inclusion of ambient light sensing provides a reduction in battery power usage, which is important given the introduction of power hungry color LCD displays. Studies have shown that backlighting is only required about 40% of the time. If there is a way to automatically adjust the backlighting (such as by autodimming) to be on only when needed, considerable power savings can be achieved.
The ideal ambient sensor to save the most battery power is a sensor which has same spectral response as the human eye spectral response (V-lambda). Although this ideal ambient light sensor can be technically fabricated by using multilayered dielectric filter technology, the high cost associated with such dielectric filter technology presents a cost barrier for its use in cost demanding consumer display applications, especially in mobile devices. Therefore, a large number of the current ambient light sensor products on the market are using low cost filters which have broader spectral responses, especially into IR (Infra Red) ranges, than the human eye spectral response. Because of this spectral broadness, these ambient light sensors cannot save the battery power as wanted.
References (incorporated herein by reference in their entirety):
TAOS066G, Product brochure for TSL2562, TSL2563 Low-Voltage Light-to-Digital Converter, Texas Advanced Optoelectronic Solutions, 2007;
5988-9361EN_avago.pdf, White Paper, Ambient Light Sensing using HSDL-9000, 2006;
Osram_Appnote_for_Ambient_light_sensor_SFH—3410_and_SFH—3710, Osram Ambient Light Sensor Application Note, 2006;
AV02-0779EN.pdf, HSDL-9100 Surface-Mount Proximity Sensor, Data Sheet, Avago Technologies, 2008;
Integrated Proximity Sensor and Ambient Light Sensor, United States Published Patent Application number US 2008/0006762 A1, Jan. 10, 2008.